1. Technical Field
The present invention relates to a receiving antenna coil in which coils are wound in X-axis, Y-axis, and Z-axis directions which cross one another.
2. Related Art
A receiving antenna coil is used, as an example, by being mounted on a remote controller for locking/unlocking a keyless entry system in a car or a house. To make transmission/reception of information between a control unit on a car or house side and the controller more reliable, in recent years, improvement in a reception characteristic of the receiving antenna coil is demanded. On the other hand, to improve portability for the user, a request for miniaturization of the receiving antenna coil is also increasing.
Techniques of this kind disclosed in, for example, Japanese Unexamined Patent Publication No. 2003-92509 and WO 2007/116797 are known. FIGS. 1 and 10 of Japanese Unexamined Patent Publication No. 2003-92509 show an antenna coil in which an X-axis receiving coil and a Y-axis receiving coil are wound so as to overlap each other.
FIG. 4 of Japanese Unexamined Patent Publication No. 2003-92509 and FIG. 1 of WO 2007/116797 show an antenna coil in which a receiving coil is wound around each of cores in a cross shape.    [Patent document 1] Japanese laid-open patent publication No. 2003-92509    [Patent document 2] International patent application publication No. WO 2007/116797
However, when coils are wound so as to overlap in the crossing direction, tension at the time of winding is concentratedly applied between coil wires, and there is the possibility that an insulating film on the surface of the coil is damaged. When the insulating film is damaged and the core wire of the coil wire is exposed, short-circuit of the coil occurs, the antenna characteristic deteriorates, and it becomes a problem. When X-axis and Y-axis receiving coils are wound so as to overlap each other like in the antenna coil described in Japanese Unexamined Patent Publication No. 2003-92509, it is difficult to reduce the height in the Z-axis direction, that is, the thickness dimension.
In the case of the cross-shaped core described in WO 2007/116797, it is difficult to wind a wire at the intersecting part of the cross, so that it is difficult to assure the sufficient number of turns of the coil. Since it is generally difficult to assure large volume of a cross-shaped core in a region in a Z-axis receiving coil disposed so as to surround X-axis and Y-axis receiving coils, it is difficult to sufficiently increase the reception characteristic of the X-axis and Y-axis receiving coils. When the winding core part is set long to increase the number of turns in one direction in the inner region in the Z-axis receiving coil whose dimensions are restricted, the width of the winding core part in the other direction has to be decreased. The winding length and the core volume have the trade-off relation.
The present invention is achieved in view of the problems and an object of the invention is to provide a receiving antenna coil capable of realizing both improvement in the reception characteristic and miniaturization.